HECK YES!! I am loving Natalia so far. I'll reply separately with stuff related to actual other characters, but I just wanted to note a couple of things as a mod:

• Code name doesn't have to be related to their passions or have a more positive connotation! It's an opportunity for you the player to pick something cool and potentially thematic. Rule of fun reigns supreme around here. If you're still struggling to think of a code name when it comes time for apps, I'm happy to help you come up with one.
  
• That goes ditto for domain! Whatever you think is most fun and thematically on point is what's important. You mentioned Temples as a domain in the Discord, which I think has a ton of fun potential.
  
• You have some VERY fun ideas for her past life that I'm intrigued by and would love to discuss more. Specifically "an Oracle proclaimed early on that she was fated to marry an Aster" — this idea has such fun implications that I'd love to flesh out with you. The heavy class distinction was a big part of Hassalean society, and while it wasn't out of the question for Constellation nobility and Aster to marry, it was usually a little bit scandalous. So an Oracle diviner proclaiming that a Constellation noble is fated to marry an Aster would be a pretty big deal, and would probably have raised something of a commotion (even if these class boundaries eventually broke down on the Nashira). I'd love to hear what you had in mind in terms of how this affected her past life (was she excited to have her marriage dictated by prophecy? How did she feel about the idea of marrying one of the Aster?) and how else something so profound might have shaped her life on Hassaleh.
  (To be clear, this isn't me saying no to this idea -- it's a very hearty YES, I LOVE IT, NOW TELL ME MORE)
  
• Grief is a great commonality between her past and present lives. Like I mentioned, hell yeah we love a tragic heroine. There are plenty of opportunities for her spouse to have died tragically on the Nashira before the final battle with the Abyss.
  
• This is more of a side note, but as this is a setting born largely out of self-indulgent nostalgia, the school year in Chalra City starts in the spring, so as of game start, we'll be about one month into the new school year.

Feel free to hit me up on Discord for more discussion if that's easier, or we can keep it to this thread here! Whatever works for you. Very excited to see her AU come together!